BEHAVIORAL-EFFECTS OF THE ENTOMOPATHOGENIC FUNGUS, ENTOMOPHTHORA-MUSCAE ON ITS HOST MUSCA-DOMESTICA - POSTURAL CHANGES IN DYING HOSTS AND GATED PATTERN OF MORTALITY

Videotaped records of house flies dying from infection with the fungus Entomophthora muscae showed that flies typically die on the fourth or fifth day post-infection in elevated positions, vith the proboscis ex tended and attached to the substrate, the legs spread, the abdomen ang led away from the substrate and the wings raised above the thorax, Fou r events occurring before or shortly after death were identified, the last locomotory movement (LM), the last extension of the proboscis to the substrate (PD), the start of upward wing movement (WS) and the end of upward wing movement (WU), Progression through this sequence was e ssentially unidirectional and highly stereotyped, The median elapsed t ime between WS and WU was 15 min, The median time between LM and WU wa s 1.25 h, The mortality of diseased flies, observed over several days, exhibited a distinct diel periodicity under both natural and artifici al photoperiodic regimes with most flies dying 0-5 h before the onset of darkness. The mortality of flies held in the dark from the time of exposure until death did not exhibit rhythmicity; however, a circadian periodicity of mortality was observed in a population of infected fli es exposed to a L12:D12 photoperiod for 3 days following infection and then held in continuous darkness. These findings indicate that mortal ity in E, muscae-diseased flies is a gated phenomenon governed by a bi ological clock, that, it is argued, is most probably a property of the fungus.